1. atomic number 81 a soft grey malleable metallic element that resembles tin but discolors on exposure to air; it is highly toxic and is used in rodent and insect poisons; occurs in zinc blende and some iron ores
  2. atomic number 11 a silvery soft waxy metallic element of the alkali metal group; occurs abundantly in natural compounds (especially in salt water); burns with a yellow flame and reacts violently in water; occurs in sea water and in the mineral halite (rock salt)
  3. atomic number 88 an intensely radioactive metallic element that occurs in minute amounts in uranium ores
  4. atomic number 18 a colorless and odorless inert gas
  5. atomic number 21 a white trivalent metallic element
  6. atomic number 87 a radioactive element of the alkali-metal group discovered as a disintegration product of actinium
  7. atomic number 89 a radioactive element of the actinide series
  8. atomic number 83 a heavy brittle diamagnetic trivalent metallic element
  9. atomic number 41 a soft grey ductile metallic element used in alloys
  10. atomic number 61 a soft silvery metallic element of the rare earth group having no stable isotope; was discovered in radioactive form as a fission product of uranium
  11. atomic number 82 a soft heavy toxic malleable metallic element
  12. atomic number 84 a radioactive metallic element that is similar to tellurium and bismuth; occurs in uranium ores but can be produced by bombarding bismuth with neutrons in a nuclear reactor
  13. atomic number 85 a highly unstable radioactive element
  14. atomic number 31 a rare silvery metallic element
  15. atomic number 51 a metallic element having four allotropic forms
  16. atomic number 71 a trivalent metallic element of the rare earth group
  17. atomic number 80 a heavy silvery toxic univalent and bivalent metallic element; the only metal that is liquid at ordinary temperatures
  18. atomic number 86 a radioactive gaseous element formed by the disintegration of radium; the heaviest of the inert gasses; occurs naturally (especially in areas over granite) and is considered a hazard to health
  19. atomic number 91 a short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead
  20. atomic number 1 a nonmetallic univalent element that is normally a colorless and odorless highly flammable diatomic gas; the simplest and lightest and most abundant element in the universe